I don’t see how a leaf shutter can provide even exposure over the entire film plane. As shutter action begins, it appears that the center of the aperture is exposed first and continues to be exposed as the leaf shutter cycles to full open then close. Isn’t it true that the nature of this design must expose the center of the film plane more than the outside edges. In other words, vignetting, however slight, is inevitable.
Think of it this way. When you expose a frame with a focal plane shutter camera, and your aperture is f/1.4, you get a full frame of exposure. If you expose at f/32, you still get a full frame of exposure. A lens shutter essentially is just an additional set of aperture blades, with a range between f/wide open and f/infinity.
In reality, at moderate to long exposures, a lens shutter opens very quickly, to as wide as your lens aperture can go. Then it stays open for the timed exposure you desire. Finally, it closes very quickly. There is a lot of clever mechanical gear in there that is designed to keep the correct amount of light equalized across shutter speeds for all three parts of the cycle. It's not perfect, of course.
Some people think there is a subtle image effect that comes into play when you use relatively quick exposures. Since the time required for the blades to come open and close is a significant percentage of the full exposure time, effectively, you end up exposing the image at multiple aperture settings throughout the short time the shutter is working. So f/2.8 at 1/250 is actually partly at f/2.8, and partly at every setting down to f/64. I've often wondered if that accounts for some of the unique look we get with classic lens shutter cameras, like Rollei TLRs.
I don't sense it with my Hasselblad V cameras as much, but I think that may be because my Hasselblad lenses all have so few aperture blades that they play their own unpredictable games with the bokeh. But we get out on really thin ground when we start talking aperture blades and bokeh...
